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Growth mechanism and magnon excitation in NiO nanowalls.

Gandhi AC, Huang CY, Yang CC, Chan TS, Cheng CL, Ma YR, Wu SY - Nanoscale Res Lett (2011)

Bottom Line: The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed.This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation.Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan. sywu@mail.ndhu.edu.tw.

ABSTRACT
The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

No MeSH data available.


Related in: MedlinePlus

EDS mapping of NiO. (a) Side view of a cross-sectional NiO grid SEM image, indicating the existence of the Ni core and NiO surface at TA = 700°C, (b) Typical EDS pattern taken at the Ni core, and (c) NiO surface. (d, e) Two-dimensional EDS mapping images of the distribution of elements presented using the lock-in energy of Ni-Kα1 (7.3 to 7.6 keV) and O-Kα1 (0.4 to 0.6 keV). The inset to (e) shows a step function at both edges that can be used to define the mean diffusion length <S >.
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Figure 5: EDS mapping of NiO. (a) Side view of a cross-sectional NiO grid SEM image, indicating the existence of the Ni core and NiO surface at TA = 700°C, (b) Typical EDS pattern taken at the Ni core, and (c) NiO surface. (d, e) Two-dimensional EDS mapping images of the distribution of elements presented using the lock-in energy of Ni-Kα1 (7.3 to 7.6 keV) and O-Kα1 (0.4 to 0.6 keV). The inset to (e) shows a step function at both edges that can be used to define the mean diffusion length <S >.

Mentions: Since the NiO nanowall growth process is dependent on the surface diffusion of Ni (with respect to the annealing temperature and time), the cross-section of such a grid should look like the core-shell structure of Ni/NiO. To verify the formation of NiO nanowalls, further SEM investigation was carried out. An EDS (Inca x-sight model 7557, Oxford Instruments, UK) mapping technique was used to measure the shell thickness of NiO. EDS mapping generates a two-dimensional image indicating the abundance of an element. The intensity of the image allows direct visualization of the spatial distribution of any element, such as nickel or oxygen, on the surface of the Ni grid. Figure 5a depicts an SEM image of a cross-section of the Ni grid of the selected sample (at TA = 700°C). It can be seen that the cross-section is not uniform with the formation of the core and shell being dominated by Ni and NiO, respectively. Typical EDS elemental spectra taken at the core and shell (indicated by the white cross and circle in Figure 5a are shown in Figure 5b, c, respectively. The peaks shown in Figure 5b are associated with a series of elemental Ni which can be assigned to Ni-Lβ1, Ni-Kα1, and Ni-Kβ1 (the oxygen peak is weak and can be ignored), verifying that the core center contains only Ni element. The small peaks of Cu and C were the result of the carbon film on the Cu grid from mounting the sample. The surface shell, because of thermal activation, showed an increase in the oxygen contribution, shown in Figure 5c. Moreover, the Ni/O ratio is estimated to be 0.91(1), which is close to the stoichiometric composition of NiO, indicating the high purity of the nanowalls and the existence of nickel vacancies. Figure 5d, e show EDS mapping images of the distribution of elements presented using the lock-in energy of Ni-Kα1 (7.3 to 7.6 keV) and O-Kα1 (0.4 to 0.6 keV), respectively. The formation of NiO nanowalls can be mapped by EDS observations and the diffusion at various points along the length of the cross-section estimated. The inset to Figure 5d shows that the length (dashed line) is dependent on the intensity of the elemental oxygen. There is an evident step function on both edges of the inset of Figure 5d. The width of the step <s > enables us to define the length of diffusion of the nickel at various TA. The obtained diffusion lengths are shown in Table 3. Thermal treatment of the Ni grid is known to influence the rates of oxide growth during nucleation and nanowall formation. The diffusion length is also sensitive to the thermal treatment time. A diffusion model is employed to interpret the oxidation kinetics wherein nickel transport proceeds in nickel oxide both by short-circuit and lattice diffusion.


Growth mechanism and magnon excitation in NiO nanowalls.

Gandhi AC, Huang CY, Yang CC, Chan TS, Cheng CL, Ma YR, Wu SY - Nanoscale Res Lett (2011)

EDS mapping of NiO. (a) Side view of a cross-sectional NiO grid SEM image, indicating the existence of the Ni core and NiO surface at TA = 700°C, (b) Typical EDS pattern taken at the Ni core, and (c) NiO surface. (d, e) Two-dimensional EDS mapping images of the distribution of elements presented using the lock-in energy of Ni-Kα1 (7.3 to 7.6 keV) and O-Kα1 (0.4 to 0.6 keV). The inset to (e) shows a step function at both edges that can be used to define the mean diffusion length <S >.
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Figure 5: EDS mapping of NiO. (a) Side view of a cross-sectional NiO grid SEM image, indicating the existence of the Ni core and NiO surface at TA = 700°C, (b) Typical EDS pattern taken at the Ni core, and (c) NiO surface. (d, e) Two-dimensional EDS mapping images of the distribution of elements presented using the lock-in energy of Ni-Kα1 (7.3 to 7.6 keV) and O-Kα1 (0.4 to 0.6 keV). The inset to (e) shows a step function at both edges that can be used to define the mean diffusion length <S >.
Mentions: Since the NiO nanowall growth process is dependent on the surface diffusion of Ni (with respect to the annealing temperature and time), the cross-section of such a grid should look like the core-shell structure of Ni/NiO. To verify the formation of NiO nanowalls, further SEM investigation was carried out. An EDS (Inca x-sight model 7557, Oxford Instruments, UK) mapping technique was used to measure the shell thickness of NiO. EDS mapping generates a two-dimensional image indicating the abundance of an element. The intensity of the image allows direct visualization of the spatial distribution of any element, such as nickel or oxygen, on the surface of the Ni grid. Figure 5a depicts an SEM image of a cross-section of the Ni grid of the selected sample (at TA = 700°C). It can be seen that the cross-section is not uniform with the formation of the core and shell being dominated by Ni and NiO, respectively. Typical EDS elemental spectra taken at the core and shell (indicated by the white cross and circle in Figure 5a are shown in Figure 5b, c, respectively. The peaks shown in Figure 5b are associated with a series of elemental Ni which can be assigned to Ni-Lβ1, Ni-Kα1, and Ni-Kβ1 (the oxygen peak is weak and can be ignored), verifying that the core center contains only Ni element. The small peaks of Cu and C were the result of the carbon film on the Cu grid from mounting the sample. The surface shell, because of thermal activation, showed an increase in the oxygen contribution, shown in Figure 5c. Moreover, the Ni/O ratio is estimated to be 0.91(1), which is close to the stoichiometric composition of NiO, indicating the high purity of the nanowalls and the existence of nickel vacancies. Figure 5d, e show EDS mapping images of the distribution of elements presented using the lock-in energy of Ni-Kα1 (7.3 to 7.6 keV) and O-Kα1 (0.4 to 0.6 keV), respectively. The formation of NiO nanowalls can be mapped by EDS observations and the diffusion at various points along the length of the cross-section estimated. The inset to Figure 5d shows that the length (dashed line) is dependent on the intensity of the elemental oxygen. There is an evident step function on both edges of the inset of Figure 5d. The width of the step <s > enables us to define the length of diffusion of the nickel at various TA. The obtained diffusion lengths are shown in Table 3. Thermal treatment of the Ni grid is known to influence the rates of oxide growth during nucleation and nanowall formation. The diffusion length is also sensitive to the thermal treatment time. A diffusion model is employed to interpret the oxidation kinetics wherein nickel transport proceeds in nickel oxide both by short-circuit and lattice diffusion.

Bottom Line: The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed.This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation.Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan. sywu@mail.ndhu.edu.tw.

ABSTRACT
The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di.

No MeSH data available.


Related in: MedlinePlus